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PolarCoN project to bridge green gap

15 Jul 2008

A project looking to develop green-emitting laser diodes based on nitride materials has been awarded EURO2million in funding.

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Eight research groups across Germany and Switzerland have united under the PolarCoN banner to develop green nitride-based laser diodes. The consortium has received a total of around EURO 2 million in funding from the German Research Foundation and the Swiss National Science Foundation for phase one of the project, which will run to 2011.

"The project has many milestones," project coordinator Ferdinand Scholz from Ulm University in Germany told optics.org. "These include an optically-pumped green non-/semi-polar laser (wavelength > 500 nm) after 3 years and an electrically-pumped blue non-/semi-polar laser with low threshold density after 3 years."

Although phase one of the project will be carried out by university groups, Scholz says that Osram Opto Semiconductors has also had an input. "The idea is to get industry involved in the second phase of project," he commented. "This would be in the second three-year term, where we expect further funding if the first phase from 2008 to 2011 runs successfully."

The challenge for the partners is to close the "green gap". GaN-based green-light emitters currently have a low efficiency compared with their conventional blue and ultraviolet counterparts.

One of the obstacles is thought to be the polar character of GaN and related compounds, in particular for devices grown along the crystalline c-axis. The PolarCon partners will look to control the polarization effects in group III nitride-based heterostructures and investigate approaches that could be adopted in commercial optoelectronic devices of the future.

"As there are many epitaxial groups involved, different approaches will be studied, all focusing on material and structure optimization for green laser diodes," said Scholz. "This includes growth on different non- and semi-polar substrates and studies towards non- and semipolar free-standing GaN, device structures on those substrates for green laser emission (active quantum wells, doping etc.), growth of microstructures by selective epitaxy to achieve long wavelength emission and finally work on polarization reduced/matched c-direction growth using AlGaInN quaternary materials."

The partners involved in PolarCoN are:

•  Institute of Optoelectronics, Ulm University (co-ordinator)

•  Institute of Solid State Physics, TU Berlin

•  Institute of Applied Physics, TU Braunschweig

•  Institute of Experimental Physics, Otto-von-Guericke University Magdeburg

•  Institute of Experimental and Applied Physics, University Regensburg

•  Institut für Halbleiteroptik und Funktionelle Grenzflächen, Universität Stuttgart

•  Integrated Systems Laboratory, ETH Zürich

For further information, contact Ferdinand Scholz, Institute of Optoelectronics, Ulm University, Germany, e-mail

Author
Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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